# How do you factor by grouping ac - bc + ad - bd ?

$a c - b c + a d - b d$
$= \left(a c - b c\right) + \left(a d - b d\right)$
$= c \left(a - b\right) + d \left(a - b\right)$
$= \left(a - b\right) \left(c + d\right)$